An electrical device has a housing that includes a main body and a lid both of which are electrically conductive. The lid is fastened to a top surface of a sidewall of the main body so as to cover the main body. On at least one of a bottom surface of the lid and the top surface of the sidewall of the main body, there are formed a plurality of protrusions at predetermined positions; each of the protrusions abuts against that one of the bottom surface of the lid and the top surface of the sidewall which is opposed to the protrusion. Except at those predetermined positions where the protrusions are formed, there is provided, between the bottom surface of the lid and the top surface of the sidewall of the main body, a gap via which the internal and external spaces of the housing communicate with each other.